Single-component full-color emitting Ca6Y2Na2(PO4)6F2:Eu2+,Tb3+,Mn2+ phosphors with superior performance: color-tunable and energy transfer study.

Highly efficient single-component full-color emitting Ca6Y2Na2(PO4)6F2 (CYNPF):Eu2+,Tb3+,Mn2+ phosphors have been synthesized by a high-temperature solid-state reaction. Coupled with the Eu2+, Tb3+, and Mn2+ emission bands centered at 455 nm, 547 nm, and 580 nm, color-tunable white light can be generated. The energy transfer (ET) process from Eu2+ to Tb3+ and Mn2+ is attributed to the resonant dipole-dipole/dipole-dipole interaction mechanism with ultra-high ET efficiency (>90%). The emission color of the phosphors can be tuned from blue to yellowish green and orange with the corresponding CIE chromaticity coordinates of (0.1719, 0.1215), (0.2852, 0.4289), and (0.4752, 0.3903), respectively. Through controlling the concentration ratio of Tb3+ and Mn2+ ions, optimal white light emission can be obtained with CIE coordinates of (0.3381, 0.3353) excited at 365 nm, which is very close to the National Television Standards Committee white (0.330, 0.330). The thermal stability of the Eu2+, Tb3+, and Mn2+ codoped CYNPF phosphors has been investigated systematically. A single-component white LED (wLED) device has been fabricated by combining the CYNPF:Eu2+,Tb3+,Mn2+ phosphor with a 365 nm near-ultraviolet (n-UV) LED chip, which exhibits a high color rendering index (Ra = 80.2) along with a low color temperature of 5207 K and CIE coordinates of (0.3212, 0.3221). The results suggest that the phosphors can be used as a candidate material for single-component white phosphors for n-UV excited full-visible-spectrum wLEDs.

Blue-Green-Yellow Color-Tunable Luminescence of Ce3+-, Tb3+-, and Mn2+-Codoped Sr3YNa(PO4)3F via Efficient Energy Transfer.

Tunable blue-green-yellow emitting Sr3YNa(PO4)3F (SYNPF):Ce3+,Tb3+,Mn2+ phosphors have been prepared via a high-temperature solid-state reaction method. The structural and luminescent properties, energy transfer (ET) mechanism, and thermal quenching of the samples are investigated in detail. The ET from Ce3+ to Tb3+ and Mn2+ in SYNPF is identified as the interaction of the electric dipole-quadrupole with ET efficiencies of 81.6% and 69.3%, respectively. The critical distances for Ce3+/Tb3+ and Ce3+/Mn2+ are calculated through the spectral overlap method to be 9.54 and 10.92 Å. Under UV excitation, high-efficiency tunable blue-green-yellow emissions from Ce3+ to Tb3+ and Mn2+ can be obtained. Moreover, white light can also be achieved by adjusting the stoichiometry of Ce3+ and Mn2+ properly in the SYNPF phosphor. In addition, the temperature-dependent luminescence spectra exhibit good thermal quenching behaviors for the as-prepared phosphors. The above results suggest that SYNPF:Ce3+,Tb3+,Mn2+ phosphors can act as color-tunable emission phosphors for potential applications in WLEDs.

Enhanced efficiency of Cu2ZnSn(S,Se)4 solar cells via anti-reflectance properties and surface passivation by atomic layer deposited aluminum oxide.

Reducing interface recombination losses is one of the major challenges in developing Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. Here, we propose a CZTSSe solar cell with an atomic layer deposited Al2O3 thin film for surface passivation. The influence of passivation layer thickness on the power conversion efficiency (PCE), short-circuit current density (J sc), open-circuit voltage (V oc) and fill factor (FF) of the solar cell is systematically investigated. It is found that the Al2O3 film presents notable antireflection (AR) properties over a broad range of wavelengths (350-1000 nm) for CZTSSe solar cells. With increasing Al2O3 thickness (1-10 nm), the average reflectance of the CZTSSe film decreases from 12.9% to 9.6%, compared with the average reflectance of 13.6% for the CZTSSe film without Al2O3. The Al2O3 passivation layer also contributes to suppressed surface recombination and enhanced carrier separation. Passivation performance is related to chemical and field effect passivation, which is due to released H atoms from the Al-OH bonds and the formation of Al vacancies and O interstitials within Al2O3 films. Therefore, the J sc and V oc of the CZTSSe solar cell with 2 nm-Al2O3 were increased by 37.8% and 57.8%, respectively, in comparison with those of the unpassivated sample. An optimal CZTSSe solar cell was obtained with a V oc, J sc and η of 0.361 V, 33.78 mA and 5.66%. Our results indicate that Al2O3 films show the dual functions of AR and surface passivation for photovoltaic applications.

Color-tunable phosphor of Sr3YNa(PO4)3F:Tb3+ via interionic cross-relaxation energy transfer.

A series of color-tunable Sr3YNa(PO4)3F:Tb3+ phosphors with a fluorapatite structure were synthesized by a traditional high-temperature solid state reaction. The emitting color tuning from blue to green can be observed by gradually increasing Tb3+ concentrations, which is attributed to the enhanced cross-relaxation (CR) between Tb3+ ions, as described by (5D3, 7F6)-(5D4, 7F0). The CR process is analyzed based on the Dexter and Inokuti-Hirayama model, which is assigned to the electric dipole-dipole interaction. The energy transfer critical distance between Tb3+ ions is evaluated to be 18.1 Å. In addition, the thermal quenching mechanism of Sr3YNa(PO4)3F:Tb3+ is also investigated. At the general working temperature of an LED (423 K), the luminescence intensity still maintains 81% and 92% with the Tb3+ concentration of 10 and 30 mol%, respectively, indicating an excellent thermal quenching performance of Tb3+. Due to the good optical and thermal properties, the Sr3YNa(PO4)3F:Tb3+ phosphor can be used as a promising green emitting phosphor candidate in the field of white light applications.